A typical insulated electric power cable generally comprises one or more high potential conductors in a cable core that is surrounded by several layers of polymeric materials including a first semi-conductive shield layer (conductor or strand shield), an insulating layer (typically a nonconducting layer), a second semi-conductive shield layer (insulation shield), a metallic wire or tape shield used as the ground phase, and a protective jacket (which may or may not be semi-conductive). Additional layers within this construction such as moisture impervious materials are often incorporated.
A common means to achieve electrical conductivity is through the use of conductive carbon black in the polymeric formulations. Typically, carbon black loading in the semi-conductive polymer formulation ranges from 30 to 40 weight percent (wt %). The volume resistivity of these semi-conducting compounds is generally in the range of 10 to 105 ohm-centimeter (ohm-cm) when measured on a completed power cable construction using 1 of the methods described in the Insulated Cables Engineers Association (ICEA) specification S-66-524 (1982). Polyolefin formulations such as these are disclosed in U.S. Pat. Nos. 4,286,023, 4,612,139, and 5,556,697 and European Patent 0 420 271. However, the high carbon black loading results in high viscosity and poor cleanliness. Lower carbon black loadings are desirable to improve the extrusion processability of the semi-conductive shields while maintaining high electrical conductivity.
Thus, there remains a need for a polymeric composition useful in the preparation of semi-conductive polymer compositions, which exhibits higher conductivity at a lower filler loading than conventional conductive carbon black.